Distal femoral trial with removable cutting guide

ABSTRACT

Various embodiments of the present invention provide a distal femoral trial that allows a surgeon to cut the central box geometry of a distal femur using an implant-shaped trial. The trial includes a cutting guide that is removable from the trial and adjustable with respect to the trial. The guide is intended to control the depth and direction of the cutting instruments used to prepare the femur for a posterior stabilized implant.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/101,609, filed May 5, 2011, which is a divisional of U.S. patentapplication Ser. No. 11/316,255, filed Dec. 21, 2005, now U.S. Pat. No.7,963,968, which claims benefit to U.S. Patent Application Ser. No.60/638,185 filed Dec. 21, 2004 titled Distal-Femoral Prosthetic Trialand Resection Guide, the entire contents of the prior applications arehereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to surgical orthopaedic trialsand methods, particularly to trials and methods for preparing the distalfemur of a patient to receive a femoral prosthesis.

BACKGROUND

Patients suffering from unstable, painful knee joints where theinstability is caused by the lack or insufficiency of the posteriorcruciate ligament may be candidates for a total knee arthroplasty usinga posterior-stabilized knee prosthesis. Such an implant or prosthesisincludes a tibial component, a femoral component, and typically, amobile bearing insert (a patella component).

The tibial component is secured to a resected portion of the patient'stibia. This component has a post that receives a bearing or patellacomponent. The femoral component typically has inner intersecting flatsurfaces that interface with a surgically prepared distal femoralsurface, and an outer surface with a curvature that faces thecorresponding tibial component attached to the patient's tibia. Thefemoral component has two condylar regions with an intercondylarstabilizing housing that accepts the tibial post. These posteriorstabilized and constrained femoral implant components have a cam housingin between the condyles of the femur (or the condylar regions).

Bone from the distal femur must be removed from this area to accommodatefor this type of cam housing. This may be referred to as cutting thecentral box geometry. The housing sizes may differ for posteriorstabilized and constrained type femoral components. The sizes may alsodiffer from patient to patient and implant to implant. Therefore, adifferent amount of bone depth may need to be removed, depending uponthe patient and the type of femoral implant that will be used.

For optimum results, range of motion, and patient comfort, it isimportant that the tibial and femoral components are properly alignedrelative to the tibia and femur during implantation of the components.There are many accompanying instruments that are used to prepare thefemur, e.g., cutting blocks, reamers, saws, chisels, and trialcomponents.

Typically, the posterior bone removed from the distal femur toaccommodate the cam housing discussed above is removed using a cuttingblock and collet configuration. One example is shown and described byU.S. Pat. No. 5,819,829, the entire contents of which are herebyincorporated by reference. The cutting block is placed on the patient'sfemur with bone spikes and used to make anterior/posterior chamfer cuts.A rotary reamer is then inserted through a collet in the block toprepare the femur for the cam housing (to cut the central box geometry).A box chisel can then be used to complete the preparation. All of thispreparation is done using the cutting block as the reference guide.

Some problems encountered with the use of such a system are that oncethe surgeon has prepared the desired cuts in the femur, s/he will needto remove the cutting block and secure a femoral trial to the prepareddistal femur in order to check the fit and sizing. This trialing step isimportant to ensure that the ultimate component that is implanted fitsthe area that has been prepared. If additional preparation for the areawhere the cam housing will fit needs to be done, the trial is removed,the cutting block is re-positioned (which often requires insertion ofadditional bone spikes) and the cuts are further perfected. It ispossible that this procedure may need to be repeated more than once,causing undesired and additional bone removal or degradation during eachrepositioning step.

Moreover, when the bone is removed to receive the posterior stabilizedand constrained femoral implant components through the cutting block,the surgeon does not have a “feel” for how the cuts relate to the actualimplant because the cutting block is not shaped like the implant. It isessentially a square block.

Other systems have attempted to cut central box geometry through afemoral trial, but they have not used a constrained box geometry, whichcan be important to control the reaming instruments and to preventdamage to tissues that are not to be removed. If the trial being used acutting guide does not have a posterior ledge or stopping portion, it isnot always clear where the posterior cutting should stop. Moreover, suchsystems also fail to provide the desired adjustability that is needed inmany cases. If the cutting guide is attached at only a single positionwith respect to the trial, the surgeon is limited to preparing the boxgeometry only where the cutting guide sits. See e.g., U.S. Pat. No.4,721,104, the entire contents of which are hereby incorporated byreference.

Accordingly, there is a need in the art to provide a distal femoraltrial that allows a surgeon to cut the central box geometry of a distalfemur using an implant-shaped trial, while also providing removabilityand adjustability of the guide that controls the depth and direction ofthe cutting instruments. There is also a need for such systems thatprovide constrained box geometry. There is a further need for surgicalmethods and kits that use such a trial.

SUMMARY

Various embodiment of the present invention provide a distal femoraltrial that allows a surgeon to cut the central box geometry of a distalfemur using an implant-shaped trial. The trial includes a cutting guidethat is removable from the trial and adjustable with respect to thetrial. The guide is intended to control the depth and direction of thecutting instruments used to prepare the femur for a posterior stabilizedimplant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exploded perspective view of an assembly according toone embodiment of the invention.

FIG. 2 shows the embodiment of FIG. 1 in an assembled position.

FIGS. 3A and 3B show an example of an implant that is to be received bythe bone prepared using various embodiments of this invention.

FIG. 4 shows an example of a reamer that may be used to prepare apatient's bone in connection with various embodiments of the assembliesdescribed herein.

FIG. 5A shows a side perspective view of an alternate embodiment of atrial that may be used according to various embodiments of theinvention.

FIG. 5B shows a top plan view of an alternate embodiment of a trial.

FIG. 6 shows a side perspective view of an alternate cutting block thatmay be used according to various embodiments of the invention.

FIG. 7 shows the trial of FIG. 5 in combination with the cutting blockof FIG. 6.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a femoral trial component 12, a cutting guide 50, andretaining bolts 80, collectively referred to as assembly 10. FIG. 7shows an alternate femoral trial component 112 and cutting guide 150,collectively referred to as assembly 100. In both embodiments, the trial12, 112 is made with the same or similar proximal and anterior/posteriorbox geometry as the prosthesis that will be used so that it fits thegeometry of the surface of the femur that has already been resected. Italso has the same articulating surface as the prosthesis except thatthere is an opening to accommodate a cutting guide to prepare thecentral stabilizing/constraining box geometry. As shown in FIG. 7, thetrial may also include various cutting slots 114, allowing the trial toalso be used to prepare various resections on the femur. This feature isoptional and although only shown with response to the embodiment shownin FIG. 8, may be used on any trial made according to various aspects ofthis invention.

In a specific embodiment, the trial 12 has two condylar regions 14 andan anterior patellar region 34 with an articulating surface 36. Thecondylar regions 14 define an opening 16. This opening 16 is where thedistal femur is prepared to receive an implant having a cam thatcooperates with a tibial post. An example of the cam potion 202 of anactual implant 200 is shown in FIGS. 3A and 3B. The bone of the femurmust be prepared to make room to receive this cam 202, and the opening16 in trial 12 allows the space for instruments to pass duringpreparation.

The opening 16 defines a central portion 18 of the implant 12 that hasan anterior-most portion 22 and opening side edges 24. In the particularembodiment shown, in FIGS. 1 and 2, the opening side edges 24 defineorientation slots 20. Orientation slots 20 are adapted to receive base52 of cutting guide 50. In the particular embodiment shown, cuttingguide base 52 is defined by an outer flange 58. Edges of flange 52 mayslide into orientation slots 20 to secure trial 12 and cutting guide 50together.

The trial 12 also features one or more fixation holes 26, an example ofwhich is shown in FIG. 2. Fixation holes 26 are adapted to receive pins,screws, pegs, or another securing mechanism to secure trial 12 in placeon the patient's bone.

In a particular embodiment, the trial 12 has receiving portions 28,which are adapted to receive bolts 80. Bolts 80 are intended to securecutting guide 50 in place, explained in more detail below. Receivingportions 28 may or may not feature threads 30.

Another embodiment of trial 12 may have one or more slight indentationsat the posterior end of the trial the provide stopping points to allow apost of cutting block to sit into as it is moved into position. Forexample, the indentation could receive a movable securing pin of thecutting guide that secures cutting guide in place with respect to trial12 without the need to use bolts 80, the use of which are described inmore detail below. Further connection mechanisms may be used also; thegeneral concept is to provide a trial and a cutting block that aresecurable in a fixed position, but where that fixed position isadjustable before being secured.

A further embodiment of trial 112 is shown in FIGS. 5A and 5B. Thistrial 112 may be similar to trial 12 in that it has condylar regions andother similar features. In the particular embodiment shown, however, thetrial 112 has an opening 16 with an anterior abutment portion 116 at itsanterior-most portion. The anterior abutment portion 116 is intended toreceive a corresponding anterior abutment pin 152 of cutting block 150,shown in FIG. 6. In use, member 154 is pulled up (in the direction ofarrow “A”), which causes pin 152 to be pulled up in the same direction.This may be accomplished through the use of a spring and spring pinassembly or any other feature. If a spring and spring pin is used, theupward movement of member 154 compresses a spring 156 that rests on topof member 154 and is retained in the guide 150. When member 154 isreleased, spring 156 forces pin 152 to extend out of guide 150 to theextended position shown in FIG. 6.

In use, while member 154 is activated and pin 152 is retracted, thecutting block 150 is slid into place in the opening of trial 112 alongorientation slots 20. When the proper position has been reached, theuser releases member 154, causing pin 152 to extend from block 150. Insome embodiments, pin 152 interfaces with abutment portion 116 of trial112, as shown in FIG. 7. In even further and preferred embodiments shownin FIG. 5B, pin 152 may be received by pin receiving portion 118 tosecure pin 152 (and cutting guide 150) in place. To remove guide 150from trial 112, the member 154 is lifted back up and the guide can slideout of orientation slots 20. In a particularly preferred embodiment, thetrial 112 may have a pin receiving portion 118, as shown in FIG. 5B. Ina particular embodiment, pin receiving portion 118 captures the anteriorportion of the pin, retaining the guide assembly from anteriordislocation while allowing posterior freedom to the posterior stop (orwall capture).

The reamer used typically is side cutting, so anterior/posteriorresection is carried out until the cutter reaches both A/P stops. If thestops are positioned so that A/P freedom is not allowed, then sidecutting or resecting in an NP direction is not needed. This depends onthe size and design of the trial.

The directional limits are controlled by the length L of the block 150,as shown by “L” in FIG. 6. The shorter the length of block 150, the moreanterior/posterior movement will be allowed in orientation slots 20.

It is not required that the block 50, 150 cooperate with the trial withorientation slots 20. It should be understood that the block 50 may snapinto place or otherwise be attached to trial through other means.

The cutting guide 50, 150 is preferably a box-shaped component that isintended to guide instruments during the preparation of the femur. Thebox is preferably formed by four complete vertical sides, but it ispossible for the box to have fewer sides and sides that are of differentheights and lengths. (The term “box” is used for convenience only, andis intended to refer to a cutting guide configuration.) In aparticularly preferred embodiment, guide has a posterior wall or capture62 that acts to constrain posterior cutting.

Cutting guide 50, 150 is intended to be attached to (and removable from)the trial 12, 112 during the preparation of the internal box geometryphase of the surgery. The guide 50, 150 has an internal box 54 thataccepts a reamer, as example of which is shown in FIG. 4. The height Hof internal box may vary. In addition, the width and other dimensionsmay be varied as well to allow the guide 50 to be fitted and femoralsize specific, accommodating various box geometry depths andanterior/posterior lengths.

In preferred embodiments, more than one guide 50, 150 is provided toaccommodate various implant and patient sizes. The box geometry depthsare controlled by the height of the guide 50. As shown in FIG. 4, anexample of a reamer 210 that may be used with guide 50 has a collar 212that determines how deep the reamer can extend into bone. The collar 112is stopped by the top surface 60 of guide 50. Thus, providingvariously-sized guides 50 with different heights allows the surgeon toprepare cavities of different depths, while using the same reamer 110.

In the embodiment shown in FIG. 7, the NP direction is controlled by thelength of guide 150. In the alternate embodiment shown in FIGS. 1 and 2,the NP direction is controlled by directional limit slots 56. Theseslots 56 are adapted to receive bolts 80, if used. The medial/laterallocation of slots 56 is such that the slots 56 fit the prosthetic lugpunch hole locations 104 (shown in FIG. 3B). The slots 56 also allowguide 50 to be positioned in any desirable anterior/posterior positionon the trial 12 so that it correlates with the position and length ofthe stabilizing/constraining box geometry needed for the desiredprosthetic size. Slots 56 are adapted to receive bolts, as shown in FIG.2, in order to secure guide 50 in place.

This feature allows the surgeon to position the trial 12 as needed inthe medial/lateral position, and the position guide as needed in theanterior/posterior direction, giving the surgeon a clear view of thecuts to be made with respect to the shape and position of the ultimateimplant to be used. The bolts 80 limit the anterior/posterior movementonce the guide 50 is properly placed.

The retaining bolts 80, shown in FIGS. 1 and 2 have posts 86 with heads88 at one end and optional threads 82 at the other end. In a preferredembodiment, the bolts 80 are cannulated 84 to allow additional fixationpins to be used to further secure to the guide 50 and bolts 80 to thepatient's distal femur. If threads 82 are provided, they may cooperatewith threads 30 of receiving portions 28. In a particularly preferredembodiment, bolt heads 88 are broached to allow for the use of a hexdriver.

Another way that the NP distance that block is allowed to travel withrespect to trial can be controlled is to insert bone spikes or screwsdirectly into the distal bone, through the directional limit slotswithout the use of bolts 80 or through any other area of the trial,which would secure the assembly and eliminate the need to use bolts asA/P translation stops. An alternate embodiment would be to insert bonespikes or screw through cannulated bolts 80.

During surgery, the trial 12, 112 is placed on the distal femur afterpreparatory resections have been made to accommodate a distal-femoralprosthesis without a stabilizing/constraining, median box. Such cuts andmethods for preparing the distal femur are known in the art. The trial12, 112 is then positioned (via bone coverage and/or trialing with thetibia and/or patella) in the desired medial/lateral position and pinnedin place through one or more fixation holes 26. In a preferredembodiment, at least one fixation hole 26 is located on the patellarregion 34 (or anterior flange).

The cutting guide 50, 150 is then placed in the orientation slots 20 onopening side edges 24 of trial 12. If necessary, retaining bolts 80 arethen threaded into receiving portions 28 in the trial 12. Bolts 80 canbe tightened by a knob-style head or with a hex driver to the desiredresistance. The cutting guide 50 can be tightened in any given placealong the orientation slots 20 and along the directional-limit slots 56with the retaining bolts 80, if desired. If additional fixation isdesired, bone spikes or other securing mechanisms can be placed throughthe cannulation area 84 of bolts 80 and into the distal femur. Once thebone resections through the cutting guide 50, 150 are preformed usingknown methods, the cutting guide 50, 150 is then removed from the trial12, while the trial 12 stays in place on the patient's femur. Anynecessary trial verification may be performed before removing the trial12. If additional box geometry preparation is needed, the cutting guide50, 150 can be replaced into position, without having to re-secure it tobone, which helps prevent any bone degradation and deterioration causedby the surgery and the need to re-cut or re-position.

Changes and modifications, additions and deletions may be made to thestructures and methods recited above and shown in the drawings withoutdeparting from the scope or spirit of the invention and the followingclaims.

What is claimed is:
 1. A femoral trial and cutting guide assembly, comprising: (a) a femoral trial component comprising condylar regions separated by an opening, the opening defining a central portion with an anterior-most portion and opening side edges; and (b) a removable cutting guide adapted to be received by the opening and secured in the opening in adjustable relation to the anterior-most portion of the opening.
 2. The assembly of claim 1, wherein the cutting guide has a posterior capture.
 3. The assembly of claim 1, wherein the opening side edges comprise orientation slots that receive a base portion of the cutting guide.
 4. The assembly of claim 1, wherein the cutting guide has directional limit slots.
 5. The assembly of claim 4, wherein the directional limit slots allow the cutting guide to be adjusted with respect to the femoral trial.
 6. The assembly of claim 1, further comprising retaining bolts that are received by the directional limit slots to secure the cutting guide to the femoral trial.
 7. The assembly of claim 6, wherein the bolts are cannulated.
 8. The assembly of claim 1, wherein the femoral trial comprises one or more receiving portions that are adapted to receive ends of retaining bolts.
 9. The assembly of claim 1, wherein the cutting guide has a movable securing pin that slides into an indent in the femoral trial to retain the cutting guide within directional limits of the femoral trial.
 10. The assembly of claim 1, wherein the femoral trial has one or more fixation holes that allow it to be secured to a prepared distal femur.
 11. The assembly of claim 1, wherein the cutting guide has an internal capture adapted to receive and stop a cutting instrument.
 12. The assembly of claim 1, wherein the assembly is provided with a plurality of cutting guides in different sizes to provide different depth and anterior/posterior length options.
 13. The assembly of claim 1, wherein the trial has an anterior abutment portion and the cutting guide has a pin adapted to be received by the anterior abutment portion to secure the cutting guide in place with respect to the trial.
 14. The assembly of claim 13, wherein the cutting guide has a retractable member that activates a spring to allow the pin to be raised and lowered with respect to the cutting block and to be secured in place with respect to the trial.
 15. A method for preparing a distal femur to receive a posterior stabilized prosthesis, comprising: (a) resecting and preparing a patient's distal femur with anterior and posterior chamfer cuts; (b) positioning a femoral trial component on the distal femur, the trial component comprising (i) condylar regions separated by an opening, the opening defining a central portion with an anterior-most portion and opening side edges and (ii) a removable cutting guide adapted to be received by the opening and secured in the opening in adjustable relation to the anterior-most portion of the opening; and (c) preparing the patient's distal femur to receive a posterior stabilized prosthesis using the removable cutting guide to guide cutting instruments. 